Sung-soo has everything a man could want - a beautiful wife and children, a comfortable home and luxury car, and plenty of money in the bank. When he learns that his estranged brother, Sung-chul, has gone missing, haunting memories of their troubled past urge him to visit his brother's apartment in search of answers. Unsettled by the shabby, half-empty apartment complex, he quickly notices strange symbols inscribed under the doorbells and the terrified residents who hurriedly lock their doors at the sight of an outsider. When Sung-soo asks the next door neighbor Joo-hee about his brother, she reacts with horror, belying her initial kindness to the family in their expensive clothes and car. The disturbing visit follows Sung-soo and his family home as strange, inexplicable things start to happen - keys to their well-secured townhome go missing, and they find themselves stalked by a mysterious masked figure. Finally, the same strange symbols appear under their doorbell, this time with an ominous bloody V. With his family terrified and his own nightmares escalating out of control, Sung-soo must face his most primal fears to reveal the shocking truth behind the intensifying horror.